Studies on glucocorticoid-induced cytolysis in cultured mouse lymphoma cells, L5178Y. I. Glucocorticoid specificity and cytoplasmic receptors in sensitive and resistant cells

Effect of corticosteroids on the morphology and proliferation of two salmonid cell lines

In medium with cortisol at 5 ng/ml and greater, cells of the rainbow trout cell line, RTG-2, lost their fibroblast-like morphology and became flattened and epithelial-like. This also occurred with dexamethasone triamcinolone acetonide, and fluocinolone acetonide but not with cortisone, progesterone, estradiol, or testosterone. Maintenance in medium with cortisol but not with cortisone caused these cells to adhere more tightly to the growth surface. The addition of cortisol at 100 ng/ml to RTG-2 cultures reduced the saturation densities that were achieved after monolayers had formed but had no effect on the times to reach confluency. Cortisone had no influence on cell population growth. Neither cortisol nor cortisone altered the morphology, adhesion, or proliferation of the Chinook salmon embryo cells, CHSE-214.

Cytotoxic effects of dexamethasone restricted to noncycling, early G1-phase cells of L1210 leukemia

The cytostatic and cytolytic effects of dexamethasone were studied as functions of cell cycle position in mouse L1210 leukemia cells. To this end, the cells were separated according to size by sedimentation at unit gravity in a specially designed sedimentation chamber. The fractions were analyzed by radioautography and flow cytophotometry. The size-distributions obtained by 1g sedimentation coincided with cell-cycle age distribution. With increasing fraction number, samples highly enriched in G1, S, and G2/M cells, respectively were obtained: the smallest cells being in early G1 and the largest in mitosis. In the presence of dexamethasone (10(-6)-10(-5) M), growth slowed down after a few cell cycles and the cells accumulated in early G1 phase. Lytic cell kill by continued exposure to the drug was confined to the fractions containing the small, early G1-phase cells. These fractions were also enriched in noncycling cells that were not labeled by prolonged exposure to 3H-thymidine. After removal of dexamethasone, the cells in S and G2/M phase completed cell cycle traverse but were retarded again in the G1 and early S phase of the next division cycle. The data suggest a memory effect for previous drug exposure. It is concluded that the cytostatic and cytolytic effects of dexamethasone are separate, though not unrelated events. Cytolysis is confined to the noncycling cells that in untreated populations can exit from the dividing compartment during a transitional phase of about 60 minutes subsequent to mitotic division. The cytostatic effects potentiate cytolysis by accumulating the cells in the early G1 phase and thus increasing the probability of their transit to the G0 compartment, sensitive for drug-mediated cytolysis.

Control of cell proliferation in human glioma by glucocorticoids

Survival and proliferation of cell cultures from human anaplastic astrocytomas were shown to be enhanced by glucocorticoids with an optimal concentration of approximately 2.5 x 10(-5)M (10 micrograms/ml). The stimulation of proliferation was only observed in a clonal growth assay and was reversed as the size of individual colonies reached approximately 50 cells. Above this size, and in regular monolayer cultures, glucocorticoids were found to inhibit cell proliferation as measured by direct cell counting and incorporation of [3H] thymidine. Cultures grown to maximum cell densities in non-limiting medium conditions reached a lower terminal cell density, and had a reduced labelling index with [3H] thymidine in the presence of glucocorticoids. Although there was little difference between the actions of beta-methasone, dexamethasone and ethyl prednisolone, methyl prednisolone was found to be more effective, both in terms of stimulation of clonal growth and inhibition of growth at high cell densities. There was no evidence of cytotoxicity with glucocorticoids up to 5 x 10(-5)M (20 micrograms/ml) and it is suggested that glucocorticoids act via a normal regulatory process, perhaps enhancing cell-cell recognition.

Effects of glucocorticosteroids on cultured human skin fibroblasts. III. Transient inhibition of cell proliferation in the early growth stages and reduced susceptibility in later growth stages

An immediate depression of the rate of cell proliferation occurred upon addition of glucocorticosteroids to cultures of human skin fibroblasts in the early growth stages. A reduced sensitivity or even insensitivity of the fibroblasts to growth inhibition inhibition was found upon the addition of the steroids at later stages of cell growth, when the cell density has increased. The inhibition in the early growth stages is transient and is most pronounced if the cultured medium is not renewed. This transient inhibition is not due to the development of steroid-resistant cell lines, and resembles the effect called tachyphylaxis, as is also observed in vasoconstriction tests.

Steroid receptors and steroid response in cultured L1210 murine leukemia cells

Murine L1210 leukemia cells were cultured in the presence of various steroid hormones to determine their growth response. Cells maintained in medium containing glucocorticoids such as dexamethasone exhibit a 10--20% inhibition of growth, whereas progesterone of 17 beta estradiol produce a 40--50% inhibition of growth. The response is due to growth inhibition and not to any cytolytic effect of the steroids. L1210 cytoplasmic and nuclear extracts contain high affinity binding sites for [3H]dexamethasone, [3H]progesterone and [3H]17 beta-estradiol. Competition with various steroids indicate that estrogens bind to one class of cytoplasmic binding sites, while glucocorticoids and progestins bind to a second class of receptor sites. These receptors appear not be be completely responsible for growth inhibition since there is no correlation between the magnitude of growth inhibition and the intracellular concentration of receptor sites, and since the concentration of steroid required to cause significant growth inhibition exceeds those concentrations required to saturate the cytoplasmic receptors.

Variations in cellular sensitivity to glucocorticoids: observations and mechanisms

The spectrum of physiological, pathological, and genetic variations in sensitivity to glucocorticoids is reviewed. The receptor for these hormones is common to most mammalian tissues, and yet the responses are widely divergent. Although there may be differences in the receptors to account for some of this diversity, it is likely that it is largely due to cellular programming not involving the receptors. In addition to the intertissue differences in sensitivity, it is also clear that intra-tissue differences occur. The greatest amount of information has been accumulated with lymphoid cell systems and there are sensitivity differences to specific responses such as cell killing or effects on immunological functions. In these systems, there can be major variations in either the extent of the response (e. g., from mild growth inhibition to cellular killing) or whether any effect is observed. Further, dose requirements for certain responses can vary by several orders of magnitude. Within a given tissue there may be developmental changes in sensitivity that are not due to obvious changes in the receptor, and decreased sensitivity with aging that in some cases has been associated with changes in receptor binding activity. Finally, the cellular sensitivity can either be influenced by hormones and other factors that affect the ability of the glucocorticoid to elicit a particular response (in a synergistic or antagonistic manner), or the same function regulated by the glucocorticoid can be inducible by the steroid, appearing some time after administration of the steroid and disappearing after steroid removal. Genetic variations in sensitivity to glucocorticoids also occur. In humans these may be generalized, affecting glucocorticoid action in all responsive tissues, and could be important in the pathogenesis of certain diseases. Perhaps the most striking genetic alterations, however, are observed in cultured lymphoid and fibroblastic cells and in acute lymphoblastic leukaemia cells ordinarily growth inhibited or killed by the glucocorticoid. Mutant cell lines arise that are highly resistant and most of these have abnormalities in the glucocorticoid receptor. In some cases binding activity is totally lost, easily expalining the resistance. In other cases, there is a more modest reduction in binding or a change in receptor properties that give it increased or decreased nuclear and DNA binding activity. An analysis of these cell lines suggests that many of the defects are in some receptor property presently not understood that makes the receptor ineffective rather than the defect being due to the quantitative changes in receptor levels detected. The frequency of emergence of steroid-resistant cells can vary widely from about 10(-5) in S49 cells to less than 10(-8) in certain thymic cell lines...

Does dexamethasone inhibit the growth of human gliomas?

Dexamethasone (10-(4)M) was shown to inhibit the growth of human gliomas in culture. This was indicated by the inhibition of incorporation of radioactively labeled thymidine into the deoxyribonucleic acid (DNA) of the cells, and by the increase in the generation time of cells exposed to the drug in vitro. On the other hand, tumors obtained from patients who had received dexamethasone before craniotomy grew considerably faster in vitro than tumors from patients who had not been given the drug before operation.

Cytolethal effects of glucocorticoids in human lymphoblastoid cell lines

Glucocorticoid hormones penetrate rapidly into intact lymphoblastoid cells and are retained with the same high affinity and specificity as with cytoplasmic extracts. Optimal conditions for lethal glucocorticoid responses in vitro were determined for a series of human lymphoblastoid cell lines by using different glucocorticoid preparations, and steroid solvents and by varying the cell density. Kinetic studies revealed that lethal glucocorticoid effects are dose-dependent and that continuous exposure of cells to steroid is necessary for progression of lethal effects to occur. Even under optimal conditions, human lymphoblastoid cells only exhibit a marked cytolethal response to glucocorticoids at concentrations which greatly exceed both physiological and therapeutically attainable steroid levels. They are also greatly in excess of steroid levels required to saturate the cytoplasmic receptors of intact or disrupted lymphoblastoid cells. It is suggested that either lethal steroid mechanisms in vitro differ fundamentally from those in vivo or the pharmacological activity of glucocorticoids in vivo does not involve a direct cytolethal action.

The effects of glucose and cyclic GMP on RNA synthesis and nuclear morphology in starved rats

Feeding rats in diet high in glucose has been demonstrated to inhibit the induction of many enzymes, block the action of glucocorticoids, and, in general, appears to result in decreased cyclic AMP activity. We found that glucose feeding depresses both messenger RNA (mRNA) and non-mRNA synthesis. Electron microscopic examination of the nucleus revealed that glucose feeding decreases the granular component of liver cell nucleoli. It only slightly decreases liver cyclic AMP levels, but produces a sixfold elevation in levels of the cyclic AMP antagonist, cyclic GMP. Administration of bromocyclic GMP, like glucose feeding, depresses mRNA synthesis, but does not simulate the effect of the carbohydrate on nuclear morphology. In addition, glucose feeding halves liver inorganic phosphate and triples ATP levels. Phosphorylation of nuclear proteins, however, remains unaltered. Despite the antagonism between glucose feeding and glucocorticoid activity, the former compound did not change the binding of dexamethasone to liver nuclei.